Metal-Induced Oxygen Diffusion-Aware Design of a-IGZO TFTs for Boosting Performance

Ultrathin IGZO thin-film transistors (TFTs) are actively investigated for high-density integration. However, excessive thinning of channels faces limitations of reduced mobility caused by trap-limited conduction (TLC), originating from an increased interface-to-bulk ratio. To overcome this limitation, we propose a metal capping layer applied to an ultrathin IGZO (3 and 5 nm), which simultaneously enhances mobility and on/off current ratio. In this work, we comprehensively investigate intrachannel conductivity variation through cross-verified I-V and C-V measurements. The gate-induced carrier modulation was extracted with (127 nF/cm²) and without (53 nF/cm²) capping via a de-embedding process, quantitatively confirming its dependence on capping length and thickness. Crucially, we reveal that the conductivity enhancement is governed by a combination of intrinsic film resistance and capping-induced effective channel length reduction during transmission line method (TLM) extraction, demonstrating that conduction paths are highly dependent on device thickness. The structural and chemical evolution at the metal capping/IGZO interface was elucidated using scanning transmission electron microscopy (STEM). Ultimately, the bulk carrier concentration improvement induced by the metal capping in ultrathin films offers a promising pathway for next-generation, high-density oxide semiconductor applications.